Up to the present time there have been many different types of apparatus designed for carbonating water for use in beverages. Some of these devices use a container of pressurized carbon dioxide which is injected into the water by various means within a carbonation chamber. Other devices do not use an existing supply of carbon dioxide but generate the carbon dioxide within the device as needed to carbonate each new batch of water and then transfer the carbon dioxide to a carbonation chamber with water therein.
In any batch type carbonating device it is desirable that the steps of generating the carbon dioxide and carbonating the water take place as rapidly as possible so that there is not an undue wait for carbonated water when it is needed for mixing a beverage.
If both the generation of carbon dioxide and the carbonation of the water occur at a rapid rate, this means that the entire batch process requires a minimum amount of time, thus eliminating any long waiting period whenever carbonated water is needed.
U.S. Pat. No. 4,040,342 issued to R.R. Austin et al. is an example of an earlier design of carbonating apparatus which both generates the carbon dioxide and carbonates the water in the same machine. In this device carbon generating chemicals are released by a certain mechanism into water in a carbon dioxide generator chamber and then the carbon dioxide is transferred into a carbonation chamber where it is injected into the water to be carbonated. While this device may perform the carbonation operation, it does not address the problem of of rapid carbon dioxide generation and rapid carbonation of the water.
For a home water carbonating apparatus to be acceptably convenient to a consumer, the time required to make one batch should be five minutes or less which is about the amount of time it takes to prepare a pot of coffee. The shorter the prepartion time, the better and more convenient it is to the user.
To achieve rapid reaction and generation of carbon dioxide gas and to simultaneously achieve rapid solvation of the carbon dioxide into the water, several conditions must be met. First, the surface area in sq. cm. divided by volume in cu. cm. of the carbonating powder or pellets must be a ratio of about 0.86 or more. The higher the exposed surface area is as a ratio of the carbon dioxide powder or pellet volume, the faster the reaction will be when the powder or pellets are submerged in water. The Austin et al. patent makes no provision for increasing the area of surface contact between the carbon generating compound and the water.
It is also necessary to cause a high percentage of the gas being injected into the water to dissolve into the water during the injection process. It is known that carbon dioxide solubility in water increases as pressure increases. An injection pressure of 120 psi, (8.437 kg/cm.sup.2) or more causes rapid solvation of the carbon dioxide into the water. The Austin et al. patent does not specify an injection pressure, however since there is no fluid restriction shown in the dispense line of the Austin et al. patent, it would seem to indicate that the tank pressure is not above 50 psi (3.516 kg/cm.sup.2) otherwise a fluid restricter would be needed to prevent the carbonated water from losing carbon dioxide gas due to a rapid pressure drop while dispensing carbonated water from the tank.
It is known that for a given gas which is soluble or partially soluble in a given liquid, (i.e., carbon dioxide and water) the rate of solvation of the gas into the liquid increases as the interfacial area between a given volume of the liquid and the gas is increased per given unit of time. For example, far more oxygen dissolves per unit of time into water cascading over a turbulent waterfall than dissolves into the equivalent volume of still water in a pond or lake in the same length of time.
In addition to that shown in Austin et al., various other methods of carbonating water are know in the prior art. In one such method carbon dioxide gas is injected into the water to be carbonated at a low level forming bubbles which float up through the water to the surface so that carbon dioxide in the bubbles becomes absorbed into the water. This method is often used in small carbonating apparatus for home use where only a limited number of drinks are mixed. Examples of this injection method of carbonation can be seen in UK Patent Specification No. 412,849 (Schwendimann) and U.S. Pat. No. 2,826,401 (Peters). The main problem with this injection method is that it is only effective if relatively high pressures are used in the carbonation chamber during carbonation.
A second known method of carbonating water involves spraying or atomizing the water into an atmosphere of carbon dioxide gas. In this method a carbonation chamber may be prefilled with carbon dioxide and the water introduced into the chamber by spraying or the chamber may be partially filled with water and the water drawn upwardly and sprayed into the carbon dioxide atmosphere above the water level in the chamber. In this method, carbon dioxide is dissolved into the water droplets in the spray and the droplets carry the carbon dioxide in dissolved form into the body of water to effect carbonation. Typical examples of this method are shown in U.S. Pat. No. 2,306,714 (Rowell) and U.S. Pat. No. 2,391,003 (Bowman). A major problem with this method is that it requires the carbonation chamber to be pressurized to a relatively high pressure and a long time is required to achieve sufficient carbonation.
A third known method of carbonation, shown in U.S. Pat. No. 4,719,056 (Scott), involves partly filling a carbonation chamber with water and providing an atmosphere of carbon dioxide above the level of water in the chamber and continuously or repeatedly drawing or forcing gas from said atmosphere down into the water by a rotating member such as a paddle wheel which rotates about a horizontal axis at 1,000 to 1,500 RPM and passes through both the carbon dioxide atmosphere and the water. This mechanical mixing increases the area of interface exposure between the carbon dioxide and water; i.e., in comparison to no mixing and causes the water and carbon dioxide to form a solution far more rapidly and to a greater solution concentration than would occur if there were no such mixing of the gas and water. The main disadvantages of this method is that it requires more moving parts, has more chance of malfunction and requires more energy to operate.
It is also known that the carbon dioxide gas solubility rate and dissolved gas concentration level in water increases as the pressure acting upon the liquid gas mix increases.
Finally, within limits, as the temperature of water decreases, the amount of carbon dioxide that can be dissolved into a given volume of water increases. This relationship is shown in Table 10-1 entitled "Solubility of Gases in Water" page 10-4 Langs Handbook of Chemistry 12th Edition. This table shows the solubility of carbon dioxide in milliliters per gram of water to be 0.759 ml at 30.degree. C. (72.degree. F.) and 1.646 ml at 1.degree. C. (34.degree. F.) showing 216 percent more carbon dioxide may be dissolved into the water at 1.degree. C. than at 30.degree. C.
The ideal process, therefore, for rapidly carbonating water with maximum levels of dissolved carbon dioxide would provide for:
a means to rapidly generate carbon dioxide PA1 a means to cause high interfacial contact between the water and carbon dioxide; PA1 a means to carry out the process at elevated pressure; and PA1 a means to carry out the process with water temperatures where the carbon dioxide gas solution level is highest; i.e., a water temperature range of 1.degree. to 5.degree. C.
The present invention satisfies these conditions at low cost and without the use of mechanical mixers or motors as will be explained later in the specification.